New York, Aug. 1: The 46-year stand-off between Cuba and America has taken a turn for the worse after Washington appointed a “transition co-ordinator” to hasten the downfall of President Fidel Castro.

Condoleezza Rice, the US secretary of state, chose Caleb McCarry to “accelerate the demise of Castro’s tyranny” on the Caribbean island that the Communist dictator has run since a coup in 1959.

The appointment is part of President George W Bush’s plan to tighten the 40-year programme of sanctions against Cuba. In addition, the American government has been beaming in extra aircraft-transmitted radio and television broadcasts to Cuba to avoid Castro’s jamming of Miami-based ones.

Over the weekend, both Cuba’s government and the dissidents it has repressed criticised the appointment, which was made last week. President Castro called the move “especially aggressive”.

“Surely he will receive a juicy salary in his new job, but Caleb McCarry ' I assure you ' will retire without setting foot in Cuba,” Felipe Perez Roque, the Cuban foreign minister, said.

Cuban dissidents have been subject to a government crackdown in recent weeks, with dozens of arrests. President Castro called them “mercenaries”, “traitors”, “bums” and “delinquents” in a speech last week. But they do not approve of the latest American move.

“Any transition in Cuba is for Cubans to define, lead, organise and co-ordinate,” said Oswaldo Paya, leader of the Christian Liberation Movement and promoter of a petition seeking democracy in Cuba.

“It will allow the Cuban government to raise the spectre of foreign interference in the internal affairs of our country,” said Elizardo Sanchez, of the National Reconciliation Commission, a dissident group.

The antagonism between America and Cuba is fostered by James Cason, the senior American official in Havana and head of the US Diplomatic Interests Section in Cuba, who has consistently denounced President Castro through his three-year stint, which ends next month.

At Christmas, he erected a large illuminated sign in his garden reading “75”, a reference to 75 pro-democracy activists imprisoned by President Castro in 2003.

Castro’s government tried to embarrass Cason by creating a cartoon character that depicts him as a fairy with a wand who turns into a rat. But Cason said: “[Castro’s] idea backfired. I’ve become an icon.”